Current methods for measuring volatile organic chemicals (VOCs) and other pollutants in the field generally involve sample collection and subsequent analysis in a well-equipped analytical chemistry laboratory. This process is time consuming and relatively expensive. For example, metropolitan water utility districts take thousands of water samples each year and perform tens of thousands of tests on those samples to determine the quality of the water (i.e. whether it meets current drinking water standards), and to check for potentially harmful substances. Additionally, tens of thousands of sites containing toxic chemical spills, leaking underground storage tanks, and chemical waste dumps require accurate characterization and long-term monitoring to reduce health risks and ensure public safety.
There exists a need for rapid, simple on-site analysis capability with high sensitivity and selectivity for detecting particular VOCs in fluids (e.g. air and ground water). The present invention provides an advance in the art to address this need by providing, in combination, a chemical preconcentrator which selectively sorbs (i.e. absorbs or adsorbs) VOCs from a liquid, gas or vapor and which, upon command, can subsequently release the absorbed or adsorbed VOCs in a concentrated whiff (i.e. a puff or plume) so that one or more chemiresistors (defined herein as chemically-sensitive resistors wherein the resistance varies in proportion to one or more chemical species to which the chemically-sensitive resistors are exposed) can detect and characterize particular VOCs in the concentrated whiff.
An advantage of the present invention is that an improved sensitivity and selectivity for sensing of VOCs is provided by the combination of the chemical preconcentrator and the chemiresistor(s) as compared to the use of chemiresistors alone.
Another advantage is that background correction for the response of the chemiresistor(s) is simplified by providing the VOCs to the chemiresistor(s) in a concentrated whiff over a short period of time.
A further advantage of the present invention is that the chemical preconcentrator can be separated from and located distal to the chemiresistor(s) to accumulate a VOC sample from a fluid, and then can be brought into proximity to the chemiresistor(s) for the analysis of particular VOCs in the sample.
Yet another advantage of the present invention is that particular VOCs can be identified and characterized based on a decay time constant using the apparatus of the present invention.
These and other advantages of the present invention will become evident to those skilled in the art.